A nice overview of the geopolitical effect of the US drawdown of troops in Afghanistan here.
In the end, the United States will leave Afghanistan (with the possible exception of some residual special operations forces). Pakistan will draw Afghanistan back into its sphere of influence. Pakistan will need American support against India (since China does not have the force needed to support Pakistanover the Himalayas nor the navy to protect Pakistan’s coast). The United States will need Pakistan to do the basic work of preventing an intercontinental al Qaeda from forming again. Reflecting on the past 10 years, Pakistan will see that as being in its national interest. The United States will use Pakistan to balance India while retaining close ties to India.